I don't think so, however, if you want to go with a primary/backup setup using a smaller backup battery the regulators (or at least one on the smaller battery) are necessary. Recall that the regulator for the primary battery feeds a higher voltage than the backup thus causing the draw from the primary.


Here's a possible setup:

Primary: 5 cell NiMH 1650 mah (5 oz), no regulator (assuming your RX can handle a 6 volt pack with no regulator)
Backup: LiPoly 900 mah (0.4 oz) with a 5.1 volt regulator (1 oz.).

Total Weight 6.4 oz.

Since the 5 cell pack should always provide > 5.1 volts the backup will never be pulled from unless a failure on the primary.

*** DANGER ***: Note, the danger here is accidentally charging the LiPoly with the wrong charger. If you us this setup I HIGHLY recommend changing the charging plug on the LiPoly so it won't fit on your standard NiMH charger.

Personally I'd use two lithium batteries.

If you want to avoid lithium and don't mind running 4-cell packs the just run two 4-cell packs without regulators.

Keith